Now I beseech you, brethren, mark them that are causing the divisions and occasions of stumbling, contrary to the doctrine which ye learned: and turn away from them.
This, and through Romans 16:20, form an apostolic warning against false and divisive teachers whom Paul expected to trouble the unity and harmony of the church in Rome. Paul had evidently received remarkably full and accurate reports on what was happening in Rome, and there were many things for which he was no doubt thankful; but his experience had taught him that the crooked zeal of false teachers would eventually reach Rome, hence this powerful warning.
I beseech you … is like the plea in Romans 12:1, and means “I beg of you, please.”
Mark them … means “identify them,” “watch out for them,” and “be on your guard against them.” Whiteside commented thus:
Do not shut your eyes to what they are doing, nor make excuses for them, nor for any others who cause divisions and occasions of stumbling contrary to the gospel, but turn away from them. This means that the brethren should have no fellowship with them.
Apparently, at the time Paul wrote, the leadership of the congregations in Rome had been able to preserve unity; and Paul’s admonition here was given to strengthen their hands and warn them against heretical teachers already operating among the churches and sure to reach Rome in time.
 Robertson L. Whiteside, op. cit., p. 296.
For they that are such serve not our Lord Jesus Christ, but their own belly; and by their smooth and fair speech they beguile the hearts of the innocent.
The contrast here is between what the false teachers are and do on the one hand and what they pretend to be and claim on the other hand. Pretending to serve Christ, they serve themselves alone, “belly” as used here being a reference to all of the carnal and fleshly desires. They were able speakers, with a ready flow of eloquent words; and impressive rhetoric and oratory were their stock in trade. Their deceitfulness and wickedness were masked and guarded with every possible camouflage of pretended piety and devotion. Intent upon causing division as a means of drawing away disciples after themselves, these false teachers are Satan’s attack forces (the shift to present tense is to focus on the problem as it still exists), not merely for the times and places known to Paul, but for all times and places, including the present now and here.
The innocent … is Paul’s reference to the naive, unsophisticated Christian, who is inclined to receive any “good speech” as the gospel truth, no matter what sacred truth may be denied by it, and never pauses to question anything, especially if the speech is a good one, and who thus unconsciously falls into the net of the false teacher.
For your obedience is come abroad unto all men. I rejoice therefore over you: but I would have you wise unto that which is good, and simple to that which is evil.
The threat of evil teachers and their seductive operations was pointed out by Christ himself (Matthew 7:15-23), and the Saviour’s description of such persons is still the fountain source of the true knowledge concerning them. They are wolves in sheep’s clothing, being recognizable principally by their fruits. The minister, or other teacher, who scatters the flock is a wolf, regardless of his pretensions. His sheepskin garb and pretended piety cannot disguise his true status as an enemy. Paul, of course, rejoiced that until the time then present, the Roman leadership had preserved harmony and unity among the Christians; but, by Paul’s warning here, he prophetically alerted them to certain danger ahead. Paul was careful, in giving such an alert, not to insinuate that the false teachers had already arrived there, hence the first clause of this verse; but it would have been folly not to warn them.
Simple unto that which is evil … seems a little ambiguous as applied to Paul’s argument here and has been explained in various ways; but its manifest reference to a desired reaction against the wiles of false teachers gives a clue to the false teacher’s modus operandi, which was invariably grounded in a pretended superiority of knowledge and intelligence. Their views were always “advanced,” allegedly, and were represented to be very learned and complicated, and thus contrasting dramatically with the great simplicities of the true religion of Christ. As Paul wrote:
But I fear, lest by any means, as the serpent beguiled Eve in his craftiness, your minds should be corrupted from the simplicity and purity that is toward Christ (2 Corinthians 11:3).
The boldness of the false teacher is always evident in his blunt rejection of valid truth coupled with an arrogant charge of simple-mindedness against those who hold and believe it. Very well, Paul seemed to say in this place, I want you to stay simple with reference to the so-called erudition of the false teacher!
The following verse, with its reference to bruising Satan under their feet, dramatically recalls that scene in Eden where God foretold such a bruising, a thing also clearly in Paul’s mind in the verse just cited, above, and in which primeval event there existed the same element of the false wisdom still being promised by Satan and his workers. Satan promised Eve that she should be “as God, knowing good and evil” (Genesis 3:5); but the unfortunate mother of all living would have been wiser to have remained simple to the wisdom Satan offered. This is the thrust of Paul’s word here.
And the God of peace shall bruise Satan under your feet shortly. The grace of our Lord Jesus Christ be with you.
Those commentators who view this eschatologically and allege that Paul expected the end of the world shortly, miss the plain point of this verse. Murray was absolutely correct when he saw this as an allusion to Genesis 3:15. As he said:
“God of peace” in this place clearly has reference to God’s maintaining peace in the church, because of its particular relevance to the bruising of Satan. The previous verses have in view the division caused by Satan’s instruments. It is God who bruises Satan and establishes peace in contrast with conflict, discord, and division. He is therefore the God of peace. The assurance given in this verse is the encouragement to heed the admonitions. Each element is significant. God will crush Satan; he will crush him under the feet of the faithful; and he will do it speedily. The promise of a victorious issue undergirds the fight of faith.
Likewise, Hodge commented:
The apostle, in giving them the assurance of the effectual aid of God, calls him the God of peace.
Thus, the bruising of Satan is not something here promised for the remote future, but is a triumph over him to be won immediately and speedily by the Roman Christians who would have the effectual aid of God in maintaining the unity and peace of the Christians when they would be attacked by the false teachers. The entire thrust of this whole passage is not forward to the eternal judgment, but retrospective to Genesis 3:15.
The grace of our Lord Jesus Christ be with you … is another of the numerous doxologies in Romans.
 John Murray, op. cit., p. 236.
 Charles Hodge, op. cit., p. 451.
Timothy my fellow-worker saluteth you; and Lucian and Jason and Sosipater, my kinsmen.
This and the next two verses contain the greetings sent by Paul’s kinsfolk, his other fellow-workers, their host, and Paul’s amanuensis, there being no less than eight of these. Timothy, of course, was usually with the apostle when circumstances permitted it, and a great affection existed between them. Two of Paul’s epistles were addressed to him, and his name must be hailed as among the most illustrious in the Bible.
The last three names in this verse are those of Paul’s kin, of whom practically nothing is known. Regarding these three, Greathouse thought:
Lucius may be the one mentioned in Acts 13:1. Jason was once Paul’s host (Acts 17:5-9) in Thessalonica. “Sosipater” may be the longer form of “Sopater” mentioned in Acts 20:4.
The objection of some commentators to Paul’s not mentioning all of his kinsfolk in the same sentence is nullified by the fact that these three were not in Rome, but in Corinth with Paul, and were joined with Paul in sending greetings to others, including three more of the kinsfolk, who were in Rome. If this elaboration of this point seems somewhat overdone, it is to refute the insinuations which fail to take this into account. For more on this, see under Romans 16:7 and Romans 16:11.
 William M. Greathouse, op. cit., p. 286.
I Tertius, who write the epistle, salute you in the Lord.
Tertius… means “third”, many Roman names having been formed from the ordinal numbers, such as Primus, Segundus, Tertius, Quartus, Quintus, Sextus, Septimus, Octavius, etc. This Tertius was Paul’s amanuensis the person who transcribed Paul’s dictation, that usually having been the manner of Paul’s writing. He customarily wrote a few lines at the end of his epistles with his own hand as a kind of signature. However, Galatians was written entirely by himself as he said:
Ye see how large a letter I have written unto you with my own hand (Galatians 6:11).
We are indebted to Hodge for this:
In order to authenticate his epistles, he generally wrote himself the salutation or benediction at the close; 1 Corinthians 16:21, “The salutation of me, Paul, with mine own hand”; 2 Thessalonians 3:17, “The salutation of Paul with mine own hand; which is the token in every epistle: so I write.”
Tertius was a Christian, and Paul honored him by asking that he write his own salutation to the brethren in Rome, which he did in these few words. Some have wondered at Tertius’ greeting coming so far from the end of the letter; but such may be easily explained, either upon the probability that Paul wrote the rest of the: epistle himself with his own hand, or that there was a pause, or break, in the dictation at this point where the personal greetings were being included, before Paul proceeded to dictate the magnificent final doxology. Tertius’ greeting belongs here where it was placed; and the custom of modern secretaries who type their initials at the very bottom of business letters does not reflect at all against the logic and appropriateness of the placement of Tertius’ salutation.
 Charles Hodge, loc. cit.